1. Field of the Invention
This invention relates to a protective structure for protecting a joint portion, especially a boot fitted around the joint portion, of a joint shaft employed in an axle of, for example, a four wheel vehicle.
2. Description of the Related Art
FIG. 5 is a partially sectioned front elevation taken from a front side of a body, showing a principal portion of a front axle of a straddle riding type four-wheel all-terrain vehicle. In general, a front axle of a four-wheel vehicle is connected to a steering system, and the same applies to that of a four-wheel drive vehicle. The front axle employs a constant velocity joint shaft 1. The constant velocity joint shaft 1 has a main shaft 2 and a driven shaft 3, which are connected together via a joint portion (constant velocity joint) 4. The driven shaft 3 is mounted with a hub 5, to which a disc wheel (not shown) of a wheel is to be attached. A reference numeral 6 in FIG. 5 denotes a cap covering a hub nut by which the hub 5 is fixed.
In a structure of the axle shown in FIG. 5, the constant velocity joint shaft 1 is supported on a knuckle arm 7. A lower end portion of the knuckle arm 7 is connected to a lower arm (which is called a xe2x80x9csuspension armxe2x80x9d as well) 9 via a specific connecting structure 8. A strut (not shown) is fixed to an upper end portion of the knuckle arm 7. A reference numeral 10 in FIG. 5 denotes an axis of the strut to be fixed to the knuckle arm.
The constant velocity joint shaft 1 is provided thereon with a rubber covering portion 11 for protecting the joint portion 4. This covering member 11 is generally called a boot. The boot 11 is exposed to the outside, and struck in some cases by a small stone during the travel of a vehicle. In view of the matter, a protective plate 12 (shown by two-dot chain lines) for protecting the boot 11 is provided in many cases. This protective plate 12 is formed by a bent flat plate, for example, and fixed to the lower arm 9.
The related art structures showing a front portion of a body of the vehicle including a front axle are disclosed in Japanese Patent Laid-Open No. 16850/1998.
However, a protective structure formed of such a protective plate 12 has the following problems.
The lower arm 9 is usually provided on the front portion of the constant velocity joint shaft 1, i.e., on the near side of the surface of FIG. 5. The lower arm 9 is positioned lower than the constant velocity joint shaft 1 as shown in FIG. 5.
Therefore, in a protective structure in which the protective plate 12 is fixed to the lower arm 9, a distance between the protective plate 12 and joint portion 4, or a distance between the protective plate 12 and boot 11 becomes large. In addition, since the protective plate 12 has a flat plate-like shape, the boot 11 is only partially covered therewith.
Under the circumstances, the joint portion 4 and boot 11 cannot be covered satisfactorily in some cases.
In view of the designing of a suspension system, it is difficult to provide the lower arm 9 in a position close to the constant velocity joint shaft 1. Consequently, it is difficult to provide the protective plate 12 close to the constant velocity joint shaft 1 for protecting the joint portion 4 and boot 11.
Since the knuckle arm 7 required to have a certain level of rigidity, it is usually manufactured out of cast iron, and a thickness thereof is designed to a level not lower than a certain level. Due to such a heavy knuckle arm 7, the weight of a vehicle as a whole increases, and, especially, the weight under the strut, which influences the traveling performance of a vehicle, is heavy.
The present invention has been made in view of the above circumstances, and provides a protective structure for a joint portion of an axle, capable of protecting the joint portion effectively. Further the present invention provides a protective structure for a joint portion of an axle, capable of contributing to the reduction of the weight of a knuckle member.
According to an aspect of the present invention, the protective structure for a joint portion of an axle of the four wheel vehicle is adapted to protect a joint portion of a joint shaft constituting the axle and being supported on a knuckle arm forming a suspension system. The knuckle member is provided with a covering portion surrounding the joint portion in the circumferential direction of the joint shaft, the joint portion being accommodated in interior space of the covering portion. According to this structure, the joint portion is surrounded by the covering portion, so that the joint portion can be protected reliably.
In this protective structure for a joint portion of an axle, the covering portion may be molded out of an aluminum alloy into an integral body with a member for supporting a driven shaft of the joint shaft and a member for supporting a strut, to form the knuckle member. With this structure, the rigidity of the knuckle member as a whole can be structurally improved. Therefore, even when the knuckle member is made of an aluminum alloy with a reduced thickness, a required level of rigidity can be secured, so that the weight of the knuckle member can be reduced. Moreover, a manufacturing process can be simplified owing to the molding method for obtaining an integral covering member.
These objectives as well as other features and advantages of the present invention will become more apparent to those skilled in the art from the following description with reference to the accompanying drawings.